Flash x ray tube

ABSTRACT

A flash X-ray tube having two electrodes, each electrode being provided with means for effecting autoelectronic emission adapted to bring about emanation of X-rays, respectively, from the other one of the two electrodes. The electrodes are so constructed and arranged in the tube that they ensure emanation of X-rays in a specified direction.

United States Patent [191 Alexandrovich et al.

[ June 28, 1974 FLASH X-RAY TUBE l l; Ljubov Nikolaevna Khudyakova,

Sevemy Pereulok, 8, kv. 24; Veniamin Aronovich Tsukerman, ulitsa Naberezhanaya, l, kv. 1, all of Moscow; Ninel Alexeevna Dron, Kostromskol Prospekt, 22, kv. 7l, Leningrad; Galina Nikolaevna Sloeva, Prospekt Narodnogoopolechenia, 177 kv. 62,;

Leningrad; Jury Konstantinovich loffe, Budapeshtskaya ulitsa, 42, Korpus 3, kv. 103, Leningrad; Vasily Vasilievich Vasiliev,

Moskovsky Prospekt, 172, kv. 102 Leningrad, all of USSR.

[22] Filed: 'Dec. 23, 1971 [21] Appl. No.: 211,204

[52] U.S. Cl. 313/56, 313/330 [51] Int. Cl. H0lj 35/04 [58] Field of Search 313/56 [56] References Cited UNITED STATES PATENTS 1,599,989 9/1926 Dechend 313/56 Primary Examiner-Herman Karl Saalbach Assistant Examiner-Darwin R. Hostetter Attorney, 4gent, or Firm Eric H. Waters, et-al.

[ ABSTRACT A flash X-ray tube having two electrodes, each electrode being provided with means for effecting autoe-, lectronic emission adapted to bring about emanation of X-rays, respectively, from the other one of the two electrodes. The electrodes are so constructed and arranged in the tube that they ensure emanation of X- rays in a specified direction.

6 Claims, 3 Drawing Figures 3 7 5 5 4 D .6 0 "Q I .4- l 0 PATENTEDJUNZB 1914 3 821580 FIB-.7

1 FLASH X-RAY TUBE The invention relates to apparatus for generating X- rays, and, more particularly, it relates to flash X-ray tubes for incorporation in various portable X-ray apparatus.

There are known flash X-ray tubes having two electrodes, the first of these electrodes being provided with means for effecting autoelectronic emission adapted to being about emanation of X-rays by the second of these two electrodes.

In these known X-ray tubes the means for effecting autoelectronic, or cold emission is provided only on one of the two electrodes, which, consequently, serves as the cathode, whereas the other, opposite one of the two electrodes is the anode.

Short-duration flashes of X-rays are produced with the help of autoelectronic emission from the cathode when a high-voltage electric pulse of negative polarity is fed thereto. The electrons emitted by the cathode attack the surface of the anode and thus bring about emanation of X-rays.

These known flash X-ray tubes, however, are not free from serious disadvantages, particularly, when they are operated in a pulse mode with a high frequency of the train of electric pulses.

The above described known tubes require pulses of a single polarity for the supply thereof, and, therefore, the associated X-ray apparatus and, more precisely, the tube supply systems of the apparatus must incorporate rectifying means which, on the one hand, complicates.

the structure of theX-ray apparatus and increases its size, and, on the other hand, causes excessive waste of electric power.

Furthermore, the intensity of X-radiation is defined by the dissipated power, and in the above-described known'tubes, power is dissipated over the anode alone, which substantially curtails the possibility of stepping up the intensity of radiation.

It is an object of the present invention to provide a flash X-ray tube which will be fed with high-voltage electric pulses of alternating polarity.

It is another object of the present invention to provide a flash X-ray tube providing increased intensity of X-radiation produced, as well as simplification of the tube supply circuitry, and, therefore, simplification of the structure and reduction of the size of the associated X-ray apparatus.

These objects are attained in a flash X-ray tube having two electrodes, the first one of said electrodes being provided with means for effecting autoelectronic emmision adapted to bring about emanation of the X-ray by the second one of said electrodes, in which tube, in accordance with the present invention, said second electrode is also provided with means for effecting autoelectronic emission adapted to bring about emanation of X-rays by said first electrode, said electrodes being so constructed and arranged as to ensure emanation of X-rays in a specified direction.

It is preferable that said X-ray tube be so constructed that said electrodes extend along the longitudinal axis of said tube, the respective opposing face surfaces of said electrodes carrying said respective means for effecting electronic emission.

Should it be desirable to reduce the dimensions of the focus and to provide possibilities for effecting stereoscopic radiography, said opposing respective face surface of said electrodes can be disposed at an angle within a 20 to range relative a plane perpendicular to said longitudinal axis of said tube, and symmetrically in respect of said plane.

Alternatively, should it be desirable to stabilize the focus in a plane perpendicular to the direction of the propagation of the X-rays, one of said two electrodes can be made from a material transparent to X-rays, said surface of said last-mentioned electrode being coated with a layer of metal with a great atomic number.

Thanks to the herein disclosed novel structure of a flash X-ray tube, there is created the possibility of increasing the power of the tube twofold, and consequently, of stepping up the intensity of the X-ray radiation, since the power is dissipated over both electrodes of the tube. Furthermore, with the means for effecting autoelectronic emission being provided on both electrodes, it becomes possible to employ electric pulses of alternating polarity for the supply of the tube, each of the electrodes serving altematingly'as the anode and the cathode, whereby the incorporation of rectifying means becomes unnecessary, and the structure of the X-ray apparatus incorporating the tube is simplified, the overall dimensions of the apparatus being simultaneously reduced.

Additionally, the field of application of the tube is broadened. The tube can be employed now for stereoscopic radiography, as well as for determining the depth of flaws by X-ray flaw detection.

The present invention will be better understood from the following detailed description of embodiments thereof with reference to the accompanying drawings, wherein:

FIG. 1 is a longitudinal sectional view of an X-ray flash tube embodying the invention;-

FIG. 2 is a longitudinal sectional view of another embodiment of the present invention; and

FIG. 3 is a longitudinal sectional view of still another embodiment of the invention.

In the drawing, FIG. 1 shows a flash X-ray tube which comprises a glass envelope 1 containing thereinside two electrodes 2 and 3. The electrodes 2 and 3 are solderedinto the envelope 1.

The first electrode 2 is provided with means 4 for effecting autoelectronic, or cold emission, in order to make the second electrode S emanate X-rays. The second electrode 3 likewise is provided with means 5 for effectingautoelectronic, or cold emission, in order to make the first electrode 2 emanate X-rays.

The electrodes 2 and 3 are arranged for emanation of the X-rays in a specified direction as shown in FIG. 1 by arrow A.

The electrodes 2 and 3 extend along the longitudinal axis 0 O of the tube, their adjacent faces 6 and 7, respectively, facing each other and carrying the means 4 and 5 for effecting autoelectronic emission.

The means 4 and 5 are autoelectronic emitters including thin-walled tubes made from a high-heat metal foil, e. g., from tungsten foil. The foil thickness is preferably l0 to 15 microns.

Alternatively, the means 4 and 5 for effecting autoelectronic emission may be in the form of tiny needles formed on the respective faces 6 and 7 of the electrodes 2 and 3 in the course of the manufacture of the latter, the dimensions of these needles being considerably smaller than the size'of the inter-electrode gap.

of dielectric cover-plates mounted on the respective faces 6 and 7 of the electrodes 2 and 3, these coverplates facilitating autoelectronic emission at the metaldielectric junctions thus formed.

In the herein disclosed embodiment of the invention in FIG. 1, the flash X-ray tube has the electrodes 2 and 3 thereof in the form of rods having their adjacent, opposing end faces 6 and 7, respectively, disposed at angle oz=30 in respect of a plane perpendicular to the longitudinal axis 0 of the tube, symmetrically relative to this plane. The angle a may be within a 20 to 60 range.

High voltage is supplied to the electrodes 2 and 3 through leads 8 and 9, respectively, the leads being formed by the extremities of the rods projecting outside the envelope 1.

.The projections of 'the foci 10 and 11 are shown in FIG. 1 in the direction of the arrow A. The angle of spread of the X-rays is equal to Zal I In order to minimize sputtering away of the metal of the electrodes 2 and 3 and to extend the operational life of the herein disclosed tube, the internal sealed-off space 12 of the envelope 1 is filled with a lightweight gas e.g., hydrogen at low pressure. The pressure of the gas is selected for the value of the free run of the molecules of the gas to approximate the size of the interelectrode gap. Alternatively, helium may be used as the lightweight gas.

In accordance with another embodiment of the I herein disclosed flash X-ray tube, illustrated in FIG. 2, the electrodes 2 and 3 are in the form of cones. One of the electrodes, e.g., the electrode 2 is hollow and is made from a thin material transparent to X-rays, e.g., berillium, the face surface 6 of this electrode 2 being externally coated with a thin layer 13 of a metal with a great atomic number, e. g., rhenium.

The wall thickness of the electrode 2 made from berillium may be from 0.05 to 0.5 mm. The thickness of the coating 13 of the metal with great atomic number may be several microns. v

Alternatively, aluminum can be employed as the material of the electrode 2 instead of berillium.

The means 4 and 5 for effecting autoelectronic emission are, in the embodiment of the flash X-ray tube in FIG. 2,.in the form of the sharp points of the respective cones and the micro-needles formed on the externals surfaces 6 and 7 of the electrodes 2 and 3, respectively, adjacent to the sharp points thereof, in the course of the manufacture of the electrodes.

The hollow electrode 2 also serves as a window for passage of X-rays which are emitted in the direction indicated by the arrow line B.

Unlike the embodiment of the X-ray flash tube illustrated in FIG. 2, the flash X-ray tube illustrated in FIG. 3, which is the third embodiment of the present invention, has the face surfaces 6 and 7, respectively, of the electrodes 2 and 3 thereof flat and parallel to each other. The direction of the emanation of the X-rays generated by this tube is indicated by the arrows C. The means 4 and 5 for effecting autoelectronic emission are in the presentlydescribed tube in the form of dielectric cover-plates.

The flash X-ray tube illustrated in FIG. 1 operates as follows.

When a high-voltage electric pulse of negative polarity is fed to the electrode 2, and a corresponding pulse 4 of positive polarity is fed to the electrode 3, the electrode 2 acts as a cathode, and the electrode 3 as an anode. The gradient of the electric field adjacent to the external edges of the foil tubes acting as the means 4 and 5 for efiecting autoelectronic, or cold emission is sufficiently high, whereby high initial density of the autoelectronic current is provided.

The electrons emitted by the electrode 2 attack the face surface 7 of the electrode 3, making the latter emanate X-rays.

After a short while, the polarity of the high-voltage electric pulses fed to the tube is reversed, whereby the electrode 2 becomes an anode and the electrode 3 becomes a cathode. Now the electrons emitted by the electrode 3 attack the face surface 6 of the electrode 2, and the latter emanates X-rays.

Thus, during each full period of the alternating high voltage supply, the herein disclosed tube generates two short flashes of X-radiation, altematingly, at the electrodes 3 and 2. v

In thedirection of discharge of the X-.radiation, i.e., in the'direction of the arrow A, there are produced two foci 10 and 11 (two electric spots) corresponding, respectively, to the faces 6 and 7 of the electrodes 2 and 3. Provided that the spacing between the most remote points of the faces 6 and 7 of the electrodes 2 and 3 does not exceed the diameter of these electrodes, the overall dimensions of the projections of the foci 10 and 11 do not extend beyond a circle defined by the diameter of the electrode 2 and 3.

ln order to attain stereoscopic X-ray pictures, or else to provide for determination of the depth of a flaw with the help of a radiograph at X-ray flawdetection, the

spacing between the electrodes 2 and 3 should be increased to several centimetres. In this case, alternating flashes of X-radiation, displaced in space in respect of the longitudinal axis 0 O of the herein disclosed tube, can be used for X-ray stereoscopy, as Well as for locating flaws or foreign bodies deep in objects under investigation.

, However, should it be desirable to minimize the adverse effects of the spatial displacement of the foci l0 and 11 at common-type radiographyof short-duration phenomena, it is advisable to employ the second embodiment of the herein disclosed tube, illustrated in FIG. 2.

In this embodiment the electron beams emitted alternatingly by the electrodes 2 and 3 fall upon the relatively small areas of the surfaces of the electrodes 2 and 3, adjacent to'the sharp points of the cones. The emanation of the X-rays is thus effected in the direction of the arrows B, along the longitudinal axis 0 O of the tube.

The focus of the last-mentioned tube is displaced by but several millimetres, exclusively along the axis of the beam of the X-rays.

Similarly to the tube illustrated in FIG. 2, the tube illustrated in FIG. 3 effects emanation of the X-rays along the longitudinal axis 0 0 thereof, in the direction indicated by the arrows C.

In this last-mentioned tube, the displacement of the focus is also minimal and takes place exclusively along the longitudinal axis 0 O.

The last-mentioned tube, illustrated in FIG. 3, has the extended area of the face ends 6 and 7 of the electrodes 2 and 3 and can be employed for applications presenting no strict requirements as to dimensions of the focus, e.g., for medical and radiobiological research.

In order to employ flash X-ray tubes constructed in accordance with the present inventions, having small dimensions and operable at 150 kV 250 kV, the associated generator of high-voltage pulses of alternating polarity to be fed to the tube should shape high-voltage electric pulses having a steepness of the forward front thereof equal to several nanoseconds.

The inductance of the discharge circuit including the tube should ensure creation of electronic currents equal to about 500 A to 1,000 A, the pulse duration being from to 20 nanoseconds. In this case at frequencies of 500 to 1,000 periods/see, the mean current through the tube would be several milliamperes.

The alternating performance of the electrodes in the tubes of the herein disclosed type provides for increasing the power dissipated over the electrodes practically twofold. Thus, tubes constructed in accordance with the present invention offer twice as much power as the by said second electrode; said second electrode carrying sound means for effecting autoelectronic emission adapted to bring about emanation of X-rays by said first electrode; said electrodes being so constructed and arranged, as to ensure emanation of X-rays in a specified direction and means for applying electric pulses of alternating polarity to said electrodes.

2. A flash X-ray tube according to claim 1, wherein said electrodes extend along thelongitudinal axis of said tube, the respective opposing face surfaces of said electrodes carrying said respective means for effecting autoelectronic emission.

3. A flash X-ray tube according to claim 2, wherein said opposing respective face surfaces of said electrodes are disposed each at an angle within a to 60 range relative to a plane perpendicular to said longitudinal axis of said tube, and symmetrically in respect of hitherto known tubes of similar dimensions having the same size of the foci. In this way the herein disclosed tubes can be used to reduce the dimensions of the said plane.

4. A flash X-ray tube according to claim 2, wherein one of said two electrodes is madefrom a material transparent for X-rays, said face surface of said lastmentioned electrode being coated with a layer of metal with a great atomic number. I

5. A flash X-ray tube as claimed in claim 2 wherein said means for effecting autoelectronic emission comprises a thin wall tube made of high heat resistant foil on the face surface of the respective electrode.

6. A flash X-ray tube as claimed in claim 5 wherein said foil is tungsten. 

1. Flash X-ray tube comprising: an envelope; a first electrode disposed within said envelope; a second electrode also disposed within said envelope; said first electrode carrying first means for effecting autoelectronic emission adapted to bring about emanation of X-rays by said second electrode; said second electrode carrying sound means for effecting autoelectronic emission adapted to bring about emanation of X-rays by said first electrode; said electrodes being so constructed and arranged, as to ensure emanation of X-rays in a specified direction and means for applying electric pulses of alternating polarity to said electrodes.
 2. A flash X-ray tube according to claim 1, wherein said electrodes extend along the longitudinal axis of said tube, the respective opposing face surfaces of said electrodes carrying said respective means for effecting autoelectronic emission.
 3. A flash X-ray tube according to claim 2, wherein said opposing respective face surfaces of said electrodes are disposed each at an angle within a 20* to 60* range relative to a plane perpendicular to said longitudinal axis of said tube, and symmetrically in respect of said plane.
 4. A flash X-ray tube according to claim 2, wherein one of said two electrodes is made from a material transparent for X-rays, said face surface of said last-mentioned electrode being coated with a layer of metal with a great atomic number.
 5. A flash X-ray tube as claimed in claim 2 wherein said means for effecting autoelectronic emission comprises a thin wall tube made of high heat resistant foil on the face surface of the respective electrode.
 6. A flash X-ray tube as claimed in claim 5 wherein said foil is tungsten. 